Quartz glass tools having comparatively high heat resistance and high purity have been used for transporting silicon wafers and holding silicon wafers in heating furnaces. An example of such quartz glass tools is a tool for use in a vertical furnace, such as shown in FIG. 1, in which (four) wafer mount members 2 having grooved portions 3 are welded to a top plate 4 and to a base plate 5. It is necessary to form grooves in the wafer mount members with a constant pitch with high accuracy. Grooving is ordinary performed with a diamond blade. With working on quartz glass with a diamond blade, however, there is a problem that since quartz glass is a brittle material, minute concaves and convexes and microcracks are generated in the worked surface to cause damage to a silicon wafer, or various transition metal element foreign matters derived from a bonding material on the diamond blade are attached to and remain on or in the minute concaves and convexes and microcracks and are molten and diffused at the time of a heat treatment on a silicon wafer to contaminate the silicon wafer. Cleaning by lightly etching with a fluoric acid solution after cutting with a diamond blade has therefore been practiced, with the result that the grooved surface is not completely cleaned; various transition metal element foreign matters remain to cause contaminations on silicon wafers. With further etching with a fluoric acid, a problem has arisen that minute concaves and convexes based on opening of microcracks in the grooved surface are made acute such as to damage a silicon wafer.
In particular, in recent years, the degree of integration of semiconductor devices has been increased and devices such as flush memories seriously badly influenced by impurities have been developed, so that the desired purity with respect to silicon wafers cannot be ensured as long as the above-described quartz glass tool is used. Therefore a method of finishing by heat-treating a surface of a groove with a burner at an angle of 5 to 45 degrees from above the grooves (patent document 1), a method of polishing a groove surface with a polishing brush (patent document 2) and the like have been proposed. With the method in patent document 1, however, remaining of the trace of a grindstone in the grooved surface and attachment of particles of a foreign matter, glass dust or the like to the trace of the grindstone, or a change in size of the grooved portion, i.e., a groove sag, or the like have occurred. Also, with the method in patent document 2, there has been a problem such as a silicon wafer contamination problem due to remaining of the trace of a grindstone and attachment of particles of a foreign matter, glass dust or the like to the trace of the grindstone.    Patent document 1: Japanese Patent Laid-Open No. 11-349338    Patent document 2: Japanese Patent Laid-Open No. 2000